US 20040066290 A1 Abstract According to one exemplary embodiment, a system for monitoring the pressure of tires of a motor vehicle with location of the wheels comprises a monitoring element and a pressure sensor. Each pressure sensor is associated with a transmitter with which it transmits to the monitoring element a radio signal comprising sensor identification data. The system comprises a means for determining the phase shift between two radio signals transmitted at two distinct times for each wheel. The system further comprises a means for determining the rotation angle, modulo 2π, traveled by each of the wheels between the two times. The system further comprises a means for comparison between the phase shifts and the rotation angles.
Claims(15) 1. A system for monitoring the pressure of tires of a motor vehicle with location of the wheels, comprising a monitoring element, one pressure sensor per wheel i associated with a transmitter with which it transmits to the monitoring element a radio signal comprising sensor identification data, the system comprising:
a means for determining the phase shift (di) between two radio signals transmitted at two distinct times (T1 and T2) for each wheel i; a means for determining the rotation angle (Dj), modulo 2π, traveled by each of the wheels j between the two times (T1 and T2); and a means for comparison between the phase shifts (di) and the rotation angles (Dj). 2. The system as defined in 3. The system as defined in 4. The system as defined in 5. A method of identifying the locations of wheels on a vehicle, comprising:
determining phase shifts between radio frequency signals transmitted at a plurality of times from each wheel; determining rotation angles traveled by each wheel at the plurality of times; and identifying the locations of the wheels on the vehicle based on the phase shifts and the rotation angles. 6. The method of identifying a first period, in the range [T1, T1+t1] of a radio frequency reception level S1[T1, T1+t1] of the radio frequency signals; identifying a second period, in the range [T2, T2+t2] of the radio frequency reception level S2[T2, T2+t2] of the radio frequency signals, wherein t1 and t2 represent one period of the radio frequency signals; and determining the phase shifts based on the first and second periods. 7. The method of 8. The method of 9. The method of determining first wheel angles based on the phase shifts and second wheel angles based on the rotation angles; ranking the first wheel angles and second wheel angles in order to create pairs of wheel angles; and identifying the locations of the wheels based on the ranking. 10. A method of identifying the locations of wheels on a vehicle, comprising, for each of a plurality of wheels:
receiving a radio frequency signal having a periodic modulation at first and second times and determining a phase shift in the periodic modulation between the first and second times; receiving a speed signal from a wheel speed sensor; and identifying the locations of the wheels on the vehicle based on the phase shifts and the speed signals. 11. The method of for each of the plurality of wheels, receiving the speed signal at the first and second times and determining a wheel rotation angle based on the speed signals. 12. The method of 13. The method of ranking the phase shifts and wheel rotation angles in order to create pairs of wheel angles; and identifying the locations of the wheels based on the ranking. 14. The method of 15. The method of identifying a first period, in the range [T1, T1+t1] of a radio frequency reception level S1[T1, T1+t1] of the radio frequency signal; identifying a second period, in the range [T2, T2+t2] of the radio frequency reception level S2[T2, T2+t2] of the radio frequency signal, wherein t1 and t2 represent one period of the radio frequency signal; and determining the phase shifts based on the first and second periods. Description [0001] The present invention concerns systems for monitoring the pressure of tires of motor vehicles, comprising, on each wheel, a pressure sensor and a transmitter for transmitting the pressure to a monitoring element. [0002] In these systems, which are referred to in the art as tire pressure monitoring systems (TPMS), the signals transmitted by the pressure sensors include data which allow them to be identified. If the wheels of a vehicle were never changed, a simple initial entry, at the factory, of the allocation between signals and wheels would allow a determination of the location of the sensors with respect to the vehicle's chassis. This determination is necessary in order to locate defective tires. [0003] Since the wheels of a vehicle are, however, occasionally put in different positions and rotated, the problem still exists of locating the wheel on which the sensor is mounted. [0004] Some solutions have already been proposed. In particular, the Applicant describes in French Patent Application FR 0 116 368 a system for monitoring tire pressure in which rotation speeds calculated on the basis of data supplied by the sensors are compared to those determined by fixed wheel rotation speed sensors whose location is known. The latter are, in particular, antilock braking system (ABS) sensors. The ABS uses a separate sensor for each wheel that provides its angular position in the form of pulses. The latter correspond to distances traveled by the wheel (on the order of a few centimeters). [0005] It is known that the wheels of a vehicle do not all rotate at the same speed. A difference in the pressure of the tires, for example, or even in the amount of wear on the tread, results in a difference in the wheels' diameter and thus in their rotation speed. Vehicle dynamics, load distribution, and temperature are also factors influencing the rotation speeds of wheels with respect to one another. [0006] These deviations are thus utilized in order to make this determination. To that end, a calculation is made of the difference between the speed of each fixed sensor and that calculated on the basis of data supplied by the pressure sensors. It is thus possible to associate with each of the fixed sensors that pressure sensor having the lowest calculated speed deviation. This system is advantageous in that it uses existing means, i.e. at no extra cost. It has also proven to be reliable, given the quality of the fixed sensors of the antilock braking system. [0007] It is not uncommon, however, for the measured speeds to be very similar to one another. Calculation convergence is then slow, and the system's reaction time is relatively long (as long as 60 minutes). The pressure sensors are powered by batteries located inside the tires. It is desirable to limit their energy consumption as much as possible in order to increase the product's service life. A limitation of the sensors' transmission time is therefore advantageous. [0008] The Applicant has thus established as its object that of improving the means of locating wheels in a tire pressure monitoring system using a means with which the transmission time of the sensors can be reduced. [0009] According to one exemplary embodiment, a system for monitoring the pressure of tires of a motor vehicle with location of the wheels comprises a monitoring element and a pressure sensor. Each pressure sensor is associated with a transmitter with which it transmits to the monitoring element a radio signal comprising sensor identification data. The system comprises a means for determining the phase shift between two radio signals transmitted at two distinct times for each wheel. The system further comprises a means for determining the rotation angle, modulo 2π, traveled by each of the wheels between the two times. The system further comprises a means for comparison between the phase shifts and the rotation angles. [0010] According to another exemplary embodiment, a method of identifying the locations of wheels in a vehicle comprises determining phase shifts between radio frequency signals transmitted at a plurality of times from each wheel and determining rotation angles traveled by each wheel at the plurality of times. The method further comprises identifying the locations of the wheels based on the phase shifts and the rotation angles. [0011] According to another exemplary embodiment, a method of identifying the locations of wheels on a vehicle comprises, for each of a plurality of wheels, receiving radio frequency signal having a periodic modulation at first and second times and determining a phase shift in a periodic modulation between the first and second times, and receiving a speed signal from a wheel speed sensor. The method further comprises identifying the locations of the wheels on the vehicle based on the phase shifts and the speed signals. [0012]FIG. 1 is a block diagram of the system according to the present invention; [0013]FIG. 2 is a flow chart for the wheel location method; [0014]FIG. 3 is a block diagram of the system according to an exemplary embodiment; [0015]FIG. 4 shows a typical signal furnished by a pressure sensor, and its modulation envelope; [0016]FIG. 5 is a flow chart of the method for determining the rotation speed of a wheel; and [0017]FIG. 6. illustrates implementation of the method at the four wheels of a vehicle. [0018] According to one exemplary embodiment, a system for monitoring the pressure of tires of a motor vehicle with location of the wheels, comprises: [0019] a monitoring element, [0020] one pressure sensor per wheel, associated with a transmitter with which it transmits to the monitoring element a radio signal comprising sensor identification data, is characterized in that it comprises: [0021] a means for determining the phase shift between two radio signals transmitted at two distinct times T1 and T2 for each wheel, [0022] a means for determining the rotation angle modulo 2π(pi) traveled by each of the wheels between times T1 and T2, and [0023] a means for comparison between the phase shifts and the rotation angles for each of the wheels. [0024] For the means for determining the rotation angle traveled, it is preferable to use rotation speed sensors on each of the wheels, in particular those of an antilock braking system. [0025] The modulation envelope of the signal furnished by the radio transmitter accommodated in the wheel is a periodic signal whose period is a function of the rotation of the wheels. In addition, the phase shift between signals measured at two given times is an indication of the distance traveled by the wheel modulo its circumference. A means is thus available for comparison with the measurement of distance traveled, deduced from a means (such as the ABS) for determining the distance traveled by each of the wheels, which can be expressed as a rotation angle. [0026] In the comparison of distances or angles traveled between two specific times, the calculation accuracy can be increased as desired. This accuracy is a function of the time period separating the two times. Control of this accuracy is better than with the previous system, in which a speed comparison is used. The result is the time required to locate the wheels can be both much more rapid and more reliable. [0027] As is evident from FIG. 1, an assemblage having a pressure sensor [0028] Receiver [0029] A shunt [0030] At its output, the monitoring element delivers pressure data, identification data, and location data to a TPMS component [0031] The program of memory [0032] Signal [0033] By way of shunt [0034] Upon emerging from filter [0035] Microprocessor [0036] The flow chart of FIG. 2 shows the various steps of the programs of memories [0037] The method for determining the phase shift of the radio signals between times T1 and T2 is based on the following principles: [0038] The following are identified from the two signals: [0039] one complete period, in the range [T1, T1+t1], of the radio-frequency reception level S1[T1, T1+t1]; [0040] one complete period, in the range [T2, T2+t2], of the radio-frequency reception level S2[T2, T2+t2]. [0041] These signals occur in the form of tables of values extracted from memory [0042] Proceeding from these value tables, the operations comprise: [0043] a time normalization, which consists in bringing the two tables of points to an identical dimension S1_normalized and S2_normalized; [0044] calculation of a correlation function in order to determine the phase shift between the two signals:
[0045] Note that the distance P traveled, modulo one wheel revolution, is related to the angle Phi by the equation [0046] Independently of the calculation of the wheel angle based on the radio signals, the program proceeds (at 35) to calculate the distance traveled by the wheels based on the data received from the ABS sensors at times T1 and T2. At 36, the corresponding wheel rotation angles are calculated on the basis of their radius. Note that the measurement accuracy provided by the ABS sensors depends on the number of pulses per revolution. One known system, for example, counts 48 pulses per, revolution. The accuracy on a wheel 0.3 m in diameter is therefore 0.039 m. [0047] The program module of memory [0048] At 50, the wheel angles (d [0049] The comparisons between the (d [0050] The angles (d [0051] To demonstrate the usefulness of the solution, a simulation was performed. [0052] This relates to two wheels proceeding over a period of six seconds with any speed profile over that period. [0053] The hypotheses were as follows:
[0054] Between two times T1 and T2 six seconds apart, a determination was made of the phase shift D [0055] For the same six-second interval, the phase shift d [0056] The phase shift distances were calculated (in meters) for several vehicle speed values. These are summarized in the table below.
[0057] It is evident that the resulting minimum value is located in the “|D1−d1|” column, which in fact refers to the wheel referenced 1. [0058] It is also apparent from this simulation that the method allows a distinction to be made between two wheels having a radius difference as small as 0.05%. At 40 km/h the deviation between these two wheels is 0.0347 m; this is at the limit of ABS measurement accuracy, which is 0.0393. At 60 km/h it is much greater. [0059] Priority application FR 02-11843, filed Sep. 25, 2002, including the specification, drawings, claims, and abstract is incorporated herein by reference in its entirety. [0060] The system for measuring the rotation speed of a wheel [0061] Referring to FIG. 3, it comprises an assemblage having a pressure sensor [0062] Fixed receiver [0063] With this apparatus, the radio signals can be converted into digital signals and the tire pressure can be calculated. [0064] The system has, in this case downstream from demodulator [0065] Here the signal processing means comprise, in series, the following means: [0066] a filtering means [0067] acquisition means [0068] a calculation processor [0069] The system furthermore comprises at least one clock [0070] In the example under consideration, the system also uses the vehicle's onboard speedometer [0071] Referring to FIG. 4, the method consists in cyclically processing the signal proceeding from the pressure sensor transmitter, the cycle comprising an observation time span Θ during which substantially identical and successive amplitude maxima P [0072] These time spans correspond to the desired period T, from which the rotation speed will be deduced. [0073] To obtain this result, signal [0074] This can be accomplished by an analog filtering method, by selecting a filter cutoff frequency Fc that is slightly greater than the maximum wheel rotation frequency. [0075] The filtered signal is then sampled at a previously determined sampling frequency fe. In accordance with a well-known signal processing rule, this frequency is at least twice the cutoff frequency Fc. [0076] Observation time span Θ is determined based on information regarding the vehicle speed available elsewhere, for example as supplied by onboard instruments (speedometer, odometer). [0077] Specifically, if U is the latter speed in meters per second, and c is the length in meters of the wheel circumference, an estimate of wheel rotation period T is provided by the ratio c/U. With this estimate it is possible to select observation time span Θ so that it contains at least the two desired maxima: Θ=(2 [0078] After a certain number of cycles, observation time span Θ can be optimized to a lower value—based on the signal's history and a knowledge of the vehicle's speed and the location of the maximum within the period—to a value that is close to T but always greater, so that the periodic signal whose period is to be determined is entirely located therein. [0079] Once this difficulty has been eliminated, beginning at a time t0 and for the observation time period thus determined, the n sampled values P
[0080] The sorted signal is then searched for two successive substantially identical maxima P [0081] The desired period is deduced therefrom: [0082] Lastly, the wheel rotation speed between time t0 and time t0+Θ is obtained using one of the aforementioned formulae. [0083] Successive rotation speeds may be obtained by simply repeating the cycle just described. This yields a sample of the instantaneous wheel rotation speed at a specific sampling frequency Fe. [0084] Since one cycle contains at least one observation time span to which, in theory, a processing time span must be added, the cycle time-span should be a longer—and, in principle, fixed—time span. [0085] The method provides a continuous measurement of the wheel rotation speed at a frequency [0086] This frequency is variable and depends on the vehicle's speed. The higher that speed, the greater the frequency will be. The higher the vehicle's speed, therefore, the more quickly a wheel rotation speed will be available. [0087] Returning to the embodiment of FIG. 3, signal [0088] Signal [0089] At the output of filter [0090] Referring to FIG. 5, processing [0091] The program, or the method, then calculates the wheel rotation speed, which it transmits to onboard computer [0092] searching memory [0093] calculating ( [0094] calculating ( [0095] acquiring ( [0096] calculating ( [0097] initializing ( [0098] waiting ( [0099] initiating the next cycle ( [0100] It is not necessary to wait for the current cycle to end if calculation completion corresponds to the end of the current cycle. Such is the case if the observation and sample acquisition operations and the speed calculation operations are consecutive. [0101] Such is not the case for a more developed version in which the wheel rotation speed determination operations performed during cycle N correspond to samples observed and acquired during cycle N−1. [0102] The reason is that in this more developed version, the speed calculation in cycle N corresponds to observation of the signal in cycle N−1. Thus, during the time elapsed between t0+N*Θ and t0+(N+1)*Θ, the microprocessor, having acquired the n samples, calculates the rotation speed for the wheel that was activated during the time period [t0+(N−1)*Θ . . . t0+N*Θ]. [0103] In the most common situation, having one measurement system for all of a vehicle's wheels (FIG. 4) and therefore comprising a group of tire pressure sensors, there are shared signal processing means ( [0104] In the case of a tire pressure measurement system comprising four receptors of the (14a) type, for example, it is sufficient to quadruple the lowpass filter and to multiplex the inputs to the sample/blocker and the analog/digital converter. This correspondingly reduces the amount of equipment required. Referenced by
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